An ink-jet printer includes a pen in which small droplets of ink are formed and ejected from the printer pen toward a printing medium. Such pens include printheads with orifice plates with several very small nozzles through which the ink droplets are ejected. Adjacent to the nozzles are ink chambers, where ink is stored prior to ejection through the nozzle. Ink is delivered to the ink chambers through ink channels in fluid communication with an ink supply. The ink supply may be, for example, contained in a reservoir part of the pen.
For color printing, multiple colors are made available to the printer. For each color of ink there is a separate ink reservoir and ink delivery system coupled to a separate group of ink chambers and nozzles. In order to achieve high quality, high-resolution printing, these groups of nozzles are placed relatively close together on the printhead. Control of ink flow is required to prevent excess ink from being delivered to the printhead. Excess ink delivery leads to leakage, or drooling from the nozzles.
Ink-jet printer systems are affected by changes in ambient conditions, such as temperature and pressure. When the ambient temperature increases or ambient pressure decreases, air diffused throughout the ink and air bubbles present within the ink reservoir expand to cause displacement of ink. Unless this expansion is managed, the displaced ink is forced out the printhead nozzles resulting in undesired drool.
When an inkjet pen drools, one color of ink may migrate across the surface of the printhead to another color group. When ambient temperature or pressure changes, the migrated ink may be sucked back into the nozzles of another color ink. The mixing of these two ink colors causes contamination, producing poor quality printing.
Open cell foam is often used to store ink within a reservoir of an ink jet pen. In conventional foam ink storage systems, the top of the reservoir may be vented to ambient to allow equalization of pressure within the ink container to the outside air pressure. However, substantially all of the exterior surfaces of conventional foam ink storage members are in contact with the walls of the pen reservoir. Such contact between ink saturated foam and the reservoir walls creates a seal through which air is unable to pass for venting to atmosphere. When changes in ambient conditions occur to expand air in the reservoir, the expanded trapped air displaces ink and causes drool through the nozzles.
To control leakage, extra felting of the foam member has been employed. Felting is a measure of the extent to which foam is compressed. Compressing the foam decreases the pore dimensions. By increasing the felting of the foam (i.e., the amount of compression of the foam), pore size decreases and capillary force increases. A greater capillary force increases back pressure within the reservoir. An increase in back pressure within the reservoir helps to prevent drool. However, extra felting of the foam does not aid removal of air trapped within the foam. Extra felting also reduces the foam's ink storage capacity. Moreover, extra felting makes manufacturing difficult, as the foam is difficult to insert in the necessarily small reservoir.
Grooved reservoir walls have been used to prevent ink drool. The grooves create a series of interconnected channels between the foam member and the reservoir walls. Expanding air from the foam's interior diffuses into these channels and is vented out of the reservoir. However, the grooved reservoir walls can be difficult to manufacture. Additionally, grooved reservoir walls can make the walls more flexible, and the pressure exerted by the compressed foam can deform the flexible reservoir walls so that the ink-jet pen does not fit properly within the printer.
The present invention is directed to a system for storing ink in a pen reservoir, while preventing ink leakage due to a change in ambient temperature or pressure. The system comprises porous grooved foam. The porous foam is grooved on the exterior portion to provide paths for air to move to the atmosphere. Thus, air within the interior portion of the foam may expand to the grooves on the exterior portion. An atmospheric vent is in fluid communication with at least one of the grooves, thereby to vent excess air within the reservoir. The grooved foam may be used in any of a variety of ink-jet pen reservoirs and may be implemented with any foam-based pen.